This application claims priority to Japanese patent application number 2001-139093, filed May 9, 2001, Japanese patent application number 2001-288375, filed Sep. 21, 2001, and Japanese patent application number 2001-391797, filed Dec. 25, 2001, each of which are incorporated herein by reference as if fully set forth herein.
1. Field of the Invention
The present invention relates to power tools, e.g., tightening tools. In one aspect of the present teachings, techniques are described for accurately detecting the remaining battery capacity of a battery utilized to drive the power tool. In another aspect of the present teachings, techniques are described for accurately terminating a fastening operation using a tightening tool.
2. Description of the Related Art
When the battery utilized with a battery powered-tool is discharged below a certain voltage level, the battery should be recharged. In order to inform the power tool operator that the battery is due for recharging, Japanese Examined Utility Model Publication No. 4-32224 describes a power tool that provides a warning when the battery has been discharged below a certain voltage level.
The known power tool includes a light-emitting diode connected to a comparator. A voltage that is proportional to the battery voltage is input to one terminal of the comparator and a fixed reference voltage is input to the other terminal of the comparator. When the voltage that is proportional to the battery voltage exceeds the reference voltage, the light-emitting diode is not illuminated. However, when the voltage that is proportional to the battery voltage falls below the reference voltage, the output of the comparator changes, thereby causing the light-emitting diode to illuminate and warn the power tool operator that the battery is due to be recharged.
However, the battery voltage will vary greatly depending on the usage status of the power tool, e.g., whether or not current is supplied from the battery to a drive source, and whether or not a load is applied to the drive source. As a result, the battery voltage that is input to the comparator also will greatly vary depending on the usage status of the power tool. Therefore, the known power tool can not accurately detect the remaining battery capacity.
It is, accordingly, one object of the present teachings to teach techniques for accurately detecting the remaining battery capacity of a battery, e.g., utilized with a power tool.
In one aspect of the present teachings, power tools may include battery 1, drive source 2, switch 3, voltage detector 4 and comparator 5, as shown in FIG. 1. A secondary battery, such as a nickel metal hydride battery or a nickel cadmium battery, may be utilized as battery 1. Battery 1 may be, e.g., disposed within the power tool or may be disposed in a detachable battery pack.
Drive source 2 generates power using current supplied from battery 1. For example, drive source 2 may include an electric motor. The power generated by the drive source 2 is transmitted to a drive shaft of the tool. Switch 3 may selectively couple drive source 2 to battery 1. Voltage detector 4 may detect the voltage of battery 1.
Comparator 5 may be utilized to determine whether the voltage of battery 1 (or a voltage representative of the battery voltage, such as a divided battery voltage) is greater than a reference voltage. If the voltage of battery 1 falls below a certain voltage level, the output of comparator 5 preferably changes in order to initiate a process for warning the power tool operator that the remaining battery capacity is insufficient to further operate the power tool in a reliable manner. For example, if the difference between (A) the battery voltage detected when a first predetermined time has elapsed after switch 3 is turned off and (B) the battery voltage detected when second predetermined time has further elapsed exceeds a predetermined value, the warning may be given to the power tool operator. Comparator 5 may be replaced with a microprocessor or any other device that can compare two voltages and provide a logic output based upon the two voltages.
The present techniques may utilize certain one or more characteristics of battery 1 in order to determine the appropriate timing for warning the power tool operator that the remaining battery capacity is insufficient (i.e., battery 1 should be recharged before further usage). As one representative example of an appropriate battery characteristic that may be advantageously utilized with the present teachings, it is noted that the voltage of a fully charged battery 1 will quickly recover when the supply of current to drive source 2 is stopped. On the other hand, the voltage of battery 1 having a relatively low remaining battery capacity will slowly recover when the supply of current to drive source 2 is stopped.
FIG. 2(a) and FIG. 2(b) show two representative examples of changes in battery voltage when switch 3 (see FIG. 1) is turned OFF after drive source 2 has been driven for a period of time. As shown in FIG. 2(a), the voltage of the fully charged battery quickly recovers when the supply of current to the drive source is stopped. On the other hand, as shown in FIG. 2(b), the voltage of the low remaining capacity battery (i.e., a battery that has been substantially discharged) recovers more slowly when the supply of current to the drive source is stopped. That is, when the battery is fully charged (or nearly fully charged), the rate of change in battery voltage approaches zero very quickly after the supply of current to the drive source is stopped. In other words, the battery voltage will substantially recover within a predetermined period of time after the supply of current to the drive source has been stopped. However, when the remaining capacity of the battery is relatively low, the battery voltage continues to slowly increase even after the predetermined period of time has elapsed, because the battery voltage recovers more slowly when the battery is substantially discharged.
Thus, by waiting a predetermined period of time after stopping the supply of current to drive source 2 to detect the voltage of battery 1, comparator 5 can accurately detect the remaining battery capacity and start the process of warning the power tool operator that the remaining battery capacity is insufficient for further use of battery 1.
In another aspect of the present teachings, power tools may include first switch 6, which is manually operated, and second switch 7, as shown in FIG. 3. First switch 6 may be utilized to selectively start and stop the supply of current to drive source 2. Second switch 7 is intermittently turned ON and OFF in order to increase or decrease the amount of current supplied to drive source 2 per unit time. Thus, first switch 6 may serve as the main switch for starting drive source 2. Second switch 7 may serve as a FET switch for pulse width modulation (PWM) control.
In the power tool of FIG. 3, when the operator switches first switch 6 to the OFF position, comparator 5 may compare the voltage of battery 1 (or a voltage representative of the battery voltage, such as a divided battery voltage) to the reference voltage. If first switch 6 is used as the main switch for starting drive source 2, the voltage of battery 1 is detected each time the operator turns off first switch 6 (i.e., each time a power tool operation is performed). If comparator 5 is actuated by first switch 6 and a motor is used as drive source 2, comparator 5 is preferably actuated only when the first switch 6 is switched to the OFF position under the conditions in which the current to the motor and the rotating speed of the motor do not vary, or do not substantially vary.
In another aspect of the present teachings, power tools may include first display 8, as shown in FIG. 4. First display 8 may be illuminated or otherwise actuated when comparator 5 starts the process of warning the power tool operator of insufficient (low) remaining battery capacity for further usage of battery 1. Thus, first display 8 may be utilized to warn the power tool operator to replace or recharge battery 1 at the appropriate time.
Optionally, when the operator is warned of the insufficient remaining battery capacity, the power tool also may actively cut or stop the supply of current to drive source 2. Thus, the power tool may prevent the operator from performing a power tool operation using a battery that has insufficient remaining battery capacity. This feature provides two advantages. First, damage to the battery from being overly discharged can be prevented. Second, the operator is prevented from performing a power tool operation when battery 1 may not be able to adequately supply current in order to complete the power tool operation.
In another aspect of the present teachings, power tools may further include second display 9 and second comparator 10, as shown in FIG. 5. Second comparator 10 may turn ON (actuate) second display 9 when the input voltage is less than the reference voltage. For example, the battery voltage may be measured when the current to motor 2 and the rotating speed of motor 2 do not vary, or do not substantially vary. If the battery voltage (or a voltage representative of the battery voltage, such as a divided voltage) is lower or less than the reference voltage, second display 9 may be illuminated or otherwise actuated in order to warn the power tool operator that battery 1 has insufficient remaining battery capacity.
In the power tool of FIG. 5, the remaining battery capacity is determined based upon the battery voltage measured at constant current discharge rate (i.e., when the current to motor 2 and the rotating speed or load of motor 2 do not vary, or do not substantially vary). In this case, if the remaining battery capacity is low or relatively low, second display 9 is activated (e.g., illuminated). Therefore, the operator can determine whether the battery has insufficient remaining battery capacity based upon whether or not first display 8 is illuminated or actuated and whether or not second display 9 is illuminated or actuated.
If first display 8 is not illuminated but second display 9 is illuminated, an abnormal state may be indicated. For example, even though the battery is sufficiently charged and the battery voltage quickly recovers after the current supply is stopped, the battery voltage is low. Accordingly, this state may indicate that a short circuit has occurred in one or more cells of battery 1.
Further, if first display 8 is illuminated but second display 9 is not illuminated, an abnormal state also may be indicated. For example, even though the battery voltage slowly recovers after the stop of the current supply, the battery voltage may be relatively high. Accordingly, this state may indicate that e.g., the internal impedance of battery 1 has increased, thereby indicating that battery 1 has acquired a xe2x80x9cmemory.xe2x80x9d
If both first display 8 and second display 9 are illuminated, the power tool operator may determine that the remaining capacity of battery 1 is insufficient. Therefore, the power tool operator can take appropriate action in accordance with the reason for the abnormal state of battery. For instance, if a short circuit exists in one or more cells of battery 1, battery 1 should be replaced. If battery 1 has acquired a memory, a battery refreshing process may be performed (e.g., battery 1 may be completely discharged before recharging battery 1). Naturally, if the remaining battery capacity of battery 1 is insufficient, battery 1 may be recharged.
According to another aspect of the present teachings, comparator 5 may detect the voltage of battery 1 after second switch 7 is switched OFF from the ON-state. Thus, when second switch 7 is switched OFF, the remaining battery capacity of battery 1 is detected. For example, a switching circuit may be provided in order to switch second switch 7 between the ON-state and the OFF-state.
For example, the switching circuit preferably turns ON second switch 7 when the power tool operator turns ON first switch 6. Further, the switching circuit may then turn OFF second switch 7 after the voltage supplied to drive source 2 has stabilized. When second switch 7 is turned OFF, the remaining battery capacity is detected. Therefore, the remaining battery capacity can be accurately detected, because the power tool operator does not stop the supply of current to drive source 2. If first switch 6 serves as the main switch, the remaining battery capacity is detected each time a power tool operation is started. Thus, it is possible to stop a power tool operation before initiating the power tool operation if battery 1 has insufficient battery capacity to perform the power tool operation.
If drive source 2 comprises a motor, the period of time between turning ON second switch 7 and turning OFF second switch 7 is preferably equal to or greater than the time constant of the motor. Therefore, a starting current will sufficiently flow to motor 2 and the battery voltage will notably decrease. As a result, after stopping the current supply to motor 2, the change in battery voltage is readily apparent, thereby enabling accurate detection of the remaining battery capacity.
In addition, if drive source 2 comprises a motor, the switching circuit preferably turns OFF second switch 7 before the motor starts rotating. In such power tools, the remaining battery capacity may be detected before the motor starts rotating. Therefore, the battery voltage will not be affected or influenced by the additional load caused by driving a rotating motor and the remaining battery capacity can be accurately detected.
Optionally, power tools may further include a third display and a third comparator. The third comparator may turn ON or illuminate the third display when the battery voltage, which is detected after the first switch is turned ON but before the second switch is turned ON, is lower or less than a predetermined (reference) voltage. If the battery voltage detected between turning ON the first switch and turning ON the second switch is lower than the predetermined (reference) voltage (i.e., if the no-load open voltage of the battery is lower than the predetermined (reference) voltage), the third display is turned ON or illuminated, thereby warning the power tool operator of the low remaining battery capacity. In this optional embodiment, because the remaining battery capacity also can be detected using the no-load open voltage of the battery, the accuracy of the detected remaining battery capacity may be increased.
Further, if the first display is not illuminated but the third display is illuminated, an abnormal state may be indicated. For example, even though battery 1 is sufficiently charged and the battery voltage quickly recovers after the current supply is stopped, the no-load open voltage is low. In this case, this state may indicate that a short circuit has occurred in one or more cells of battery 1.
Optionally, power tools may further include a fourth display and a fourth comparator. The fourth comparator may turn ON or illuminate the fourth display when the difference between (A) the no-load open voltage of the battery and (B) a voltage measured when a predetermined time has elapsed after the second switch has been turned ON exceeds a predetermined value. In this case, if the amount of voltage decrease when the drive source is started is greater than the predetermined value, the fourth display is actuated or illuminated in order to provide a warning of low remaining battery capacity. Thus, if the remaining battery capacity is also detected based upon the amount of voltage decrease when the drive source is started, the remaining battery capacity can be more accurately determined.
In another aspect of the present teachings, an abnormal state of the battery can be determined by whether or not the first display is illuminated and whether or not the fourth display is illuminated. For example, if the first display is not illuminated but the fourth display is illuminated, an abnormal state may be indicated. That is, even though the battery is sufficiently charged and the battery voltage quickly recovers after the current supply is stopped, the amount of voltage decrease is large when the drive source is actuated (started). Therefore, this state may indicate that the internal impedance of the battery has increased, thereby indicating a memory effect. In that case, the battery may be xe2x80x9crefreshedxe2x80x9d (i.e., completely discharged) before recharging the battery again in order to eliminate the memory effect.
In another aspect of the present teachings, power tools may include a battery, a drive source, a switch, a voltage detector, a timer and a comparator. The drive source may generate power using current supplied from the battery. The switch may be disposed in a circuit that couples the battery and the drive source. The voltage detector may detect the battery voltage. The timer may count the time after the switch has been turned OFF. If the time required for the battery voltage to reach a predetermined level after the switch has been turned OFF is longer (greater) than a predetermined time, the comparator may initiate a process for providing a warning of insufficient battery capacity.
When the battery is fully charged or relatively fully charged, the time required for the battery voltage to reach the predetermined level is relatively short, because the voltage of the battery will quickly recover. On the other hand, when the battery has a relatively low remaining battery capacity, the time required for the battery voltage to reach the predetermined level is relatively long, because the voltage of the battery will slowly recover. Therefore, if the battery voltage takes a relatively long amount of time to reach the predetermined voltage after the switch has been turned OFF (i.e., greater than the predetermined time), the remaining capacity of battery is probably low. In that case, the power tool operator should be warned of the low remaining battery capacity.
These aspects and features may be utilized singularly or in combination in order to provide improved battery powered tool. In addition, other objects, features and advantages of the present teachings will be readily understood after reading the following detailed description together with the accompanying drawings and the claims. Of course, the additional features and aspects disclosed hereinbelow also may be utilized singularly or in combination with the above-described aspects and features.